In recent years, as a pointing input device of a computer, a gesture input system for inputting information corresponding to hand motions or the like has attracted attention. In order to realize the gesture input system, a technology of detecting a position of an object having a planner spread such as a hand, in a non-contact manner, is required.
An example of this type of technology is disclosed in Patent Document 1. The displacement measurement device disclosed in Patent Document 1 includes a light projecting unit which projects light having a larger spread than the surface dimension of a target object, a light receiving unit having a light receiving lens which condenses reflected light from the target object and a position detecting element located near the image formation position of the condensed reflected light; and an arithmetic processing means for calculating a displacement of the target object in a direction orthogonal to the projection axis of the light or a distance to the target object, based on an output from the light receiving unit.
Patent Document 1: JP 4-307308 A